NASA managers and engineers evaluating the latest batch of proposals for private spacecraft to carry astronauts to the International Space Station fear their choices ultimately will be limited. There are growing concerns on Capitol Hill that it will be too expensive to back more than one design. The U.S. space agency received proposals for capsules, a lifting body and perhaps other approaches to transporting humans to and from low Earth orbit. But the House of Representatives is set to consider appropriations legislation this week directing an “immediate downselect” to a single commercial crew design ...